The present invention relates generally to computer hard disk drives, and, more specifically, to inertia locks therein.
A typical computer hard disk drive includes a rotating data storage disk which is accessed by a pivoting access arm which includes a read/write access head for magnetically writing data to the disk and reading data therefrom. The access arm is typically elongate and suspends the access head on a slider to float atop the data disk as it travels in operation to access different portions of the data zone on the disk.
The access head is disposed at a distal end of the arm, with the arm having a central pivot about which it rotates over the disk, using a conventional actuator such as a voice coil motor operatively joined to an opposite proximal end of the access arm. The typical voice coil motor includes suitable windings on the arm proximal end which define a rotor, with a pair of permanent magnets being suitably mounted to the disk drive housing sandwiching therebetween the access arm proximal end to define the voice coil motor. The proximal end of the access arm is selectively moved during operation between the permanent magnets for in turn traversing the access head at the opposite distal end of the access arm radially over the data storage disk to read and write data.
When the disk drive is off, the access head is typically parked on a load and unload (L/UL) ramp located at the outer diameter of the disk to prevent inadvertent contact between the access head and the disk surface which could corrupt or damage the surface and data thereon. In an alternate embodiment, the access arm may be parked near the inner diameter of the storage disk at a conventional contact start and stop (CSS) zone for the same safety consideration.
In either design, the disk drive is subject to inadvertent shock loading such as, for example, which might occur if the disk drive is dropped to the floor. Such a shock loading may effect both linear and angular shock loads which can cause the access arm to pivot over the data zone leading to undesirable damage thereof.
In order to lock the access arm in its parked position during non-operating conditions, various types of conventional latches may be used. Some latches rely on magnetic or voice-coil principles for locking the access arm in a stationary, parked position. However, these types of latches are relatively complex and expensive.
A relatively simple and inexpensive latch is conventionally known as an inertial latch which relies on its own inertia to engage a cooperating catch on the access arm during suitable shock loading of the disk drive to prevent flotation of the access arm over the data zone. A typical inertia latch is an elongate member having a central pivot, with a hook at a distal end thereof on one side of the pivot, and a counter balance at a proximal end thereof on an opposite side of the pivot. Typically, a small spring biases the latch away from the catch during normal operation, with a suitable level of angular shock automatically overcoming the restraining spring force for allowing the latch to engage the access arm and prevent its rotation during a shock event.
Although the inertia latch is relatively simple in construction, it requires precise manufacturing tolerances and mass balance. This ensures that its center of gravity is aligned with the axis of the pivot so that only angular shock loads are effective to cause relative rotation between the latch and the access arm to engage the catch and thereby lock rotation of the access arm. Since the individual inertia latches are subject to typical manufacturing tolerances during fabrication, each latch has a statistical amount of imbalance wherein its center of gravity is not perfectly aligned with the center of the latch pivot. The practical significance of even a small amount of latch imbalance is that the latch may be ineffective for locking the access arm in a very small region of the shock envelope depending on the combination of linear and angular shock loads.
Under most combinations of linear and angular shock loading, the latch will engage the catch and lock the access arm from pivoting. However, under the right combination of linear and angular shock, the effect of the off-set center of gravity due to manufacturing tolerances will prevent the latch from engaging the catch which will lead to unrestrained travel of the access arm over the storage disk and possible damage thereto. This renders the typical inertia latch statistically uncertain.
Accordingly, an improved inertia latch is desired for eliminating uncertainty of latch effectiveness due to typical manufacturing tolerances.